Thermal circuit breaker



April 14, 1958 o. WELTER 2,635,156

THERMAL. CIRCUIT BREAKER Filed April 3, 1951 Patented Apr. 14, 1953UNITED STATES PATENT OFFICE Application April 3, 1951, Seriall No.218,940 In Switzerland January 19, 1951` 8 Claims.

An embodiment of the thermal circult breaker according to my inventionis shown by way of example in the accompanying drawing, wherein Fig. 1is a sectional side elevation; and

Fig. 2 is an end elevaton, the protection cover being removed.

In these figures, Il indicates a supporting member or socket to which ahousing 12 of insulating material is attached. A conducting lamella 13with a contact Ill is conductively connected to a terminal sealed intothe socket H. The slightly curved leaf spring member I together with aheat responsive elongated member or filament ll attached to its centralportion forms an M-shaped element. A ball [8 attached to the lower endof a heat responsive elongated member or 'filament l'l is held in arecess 19 provided in a terminal 20. The lower end of the filament ll ispassed through a slot 24 in the uppermost part of the terminal 2B andthrough a small opening 22 of the socket Il. The upper part of theterminal as well as the hole 23 of the socket I] are of, square sectionin order to prevent rotation of the terminal 28. The latter has a screwthreaded mid portion cooperating with a nut 24 for adjusting the biastension of the filament ll. The legs IGa of the U-shaped leaf spring IGare clamped into the socket ll and initially stressed in. such a waythat the contact piece 25 fixed to the cross bar of the leaf. spring IBand conductively ,connected with the filament I l is normally keptremote from the fixed contact [4, the distance between the contacts. Mand 25 being increased With increasing tension of the filament Il. Inhorizontally arrang'ed holes of the housing 12 one'V of which has squaresection, a frame 28 of insulating material is mounted slidably butunrotatably by means of its bolts 28 and 21 lthe latter of which servesas an Operating knob and is held in its rest position by a coil spring29 (Fig, 1)

The operation of this device is as follows:

By pressing on the bolt 2'! the M-shaped elements 16 and Il are movedtoward the conducting lamella |3 until contacts I4 and 25 are inelectrical contact. In this position an electric current Will flowthrough terminal |5, conducting lamella |3, contact pieces M and 25,filament Il and terminal 20, thus increasing the temperature of thefilament l '1. The leaf spring IB is held in its working position by thetension of the filament |1. With increasing temperature the filament llis extended so that at a certain point the bending tension of the leafspring |6 becomes sufiiciently large to overcome the resistance of thefil- 2 ament I'l. This position of the element IG, l'l is an unstableone. If the heating is continuedthe element l, i'l snaps back into itsend position at the right whereby the contact pieces M and 25 areseparated.

The engagement of the contact pieces 14 and 25 also takes place by asudden snapping; in this case the increasing resistance of the filamentl'l against its extension and the increasing resistance of the leafspring IG against bending are overcome by the pressure on the bolt 21 upto the point where the unstable position is reached. After that theelastic tension of the filament ll is sufiicient for a further bendingofthe leaf spring and producing a contact pressure thereby bending thelamella I 3.

By means of 'the nut 24 the bias tension of the filament is adjustable,Whereby the Circuit breaker Lnay be designed for different intensitiesat which the controlling current by heating the filament causes theopening of the switch.

The heating of the filament I? is obtained by covering one or severalcurrent carrying portions of the heat responsive member i? with anelastic, electrically insulating layer Ha on which a very thinconducting layer HZ) is applied. The insulating layer consists of asuitable artificial materia'l such as artificial resin, e. g. acetyl'cellulose which is brought to the member Il by dipping', spraying orlaminating, or any suitable means.

The` conducting layer llb consists of platinum,

gold or'carbon and the like and may be applied by cathodic evaporationor thermal evaporating to one or both surfaces of the respective portionof the filament H. This thin conducting layer Ilb is electrically heatedby a battery I'Id connected to the layer i lb by a conductor lccontaining Va.

switch Ile during the operation of the breaker whereby the respectiveportion of the member I'l is heated through the electrically insulatinglayer Ha.

I wish it to be understood that I do not desire to be limited to theexact details of construction, design and operation shown and described,as modications falling within the scope of the appended claims, will beapparent to any person skilled in the art.

I claim:

1. A thermal circuit breaker, comprising, in combination, a resi1ientmember including a cross-bar and three legs forming an M-shaped part, asupporting member in which the ends of the legs opposite the cross-barare fixed, the central leg having a length diifering from that of thetwo outer legs and the longer leg or legs being slightly arcuated. and acontrol member fixed to aeaalsc said cross-bar, the resilient memberhaving a portion exposed to the controlling temperature and being undercontrol of a high ohmic heating element.

2. A thermal circuit breaker according to claim 1, the said high ohmicheating element consisting of a thin electrically conducting layeradapted to conduct a control current, the said conducting layer beingapplied to an insulating coating covering the same portion exposed tothe controlling temperature.

3. In a thermal circuit breaker 'a supporting member and an M-shapedresilient switching member having a central leg, two outer legs and across-bar, the said central leg being adjustably fixed to saidsupporting member and the said two outer legs being clamped fast in saidsupporting member, the said central leg being shorter than the two outerlegs and being coated with an electrically insulating layer which inturn is covered with a thin electrically conducting layer adapted toconduet a control current, and the said cross'- bar carrying acontacting element and a control member.

4. In a thermal circuit breaker a supporting member of insulatingmaterial, and an M-shaped resilient switching member` having a centralleg, two outer legs and a cross-bar, the said cross-bar carrying acontact piece and being freely movable opposite a second contact piececarried by a contact spring clamped fast in the said supporting member,the said outer legs of the resilient switching member being clamped fastin said supporting member opposite the said contact spring, the saidcentral leg being adjustably fixed to said supporting member between theclamping points of the said outer legs, the said central leg beingshorter than the two outer legs and being coated with an electricallyinsulating layer which in turn is covered by a thin electricallyconducting layer adapted to conduct a control current heating the saidcentral leg in order to produce a switching over thethermal circuitbreaker.

5. In a thermal circuit breaker, a thermally operable movable switchunit, comprising, in combination, a supporting member, a slightly curvedleaf spring member mounted at one end on said supporting member; acontact member mounted on the other end of said leaf spring member; aheat responsive elongated member secured at one end to said other end ofsaid leaf spring member and at its other end to said supporting memberin the region of said one end of said slightly curved leaf springmember, said heat responsive elongated member changing its lengthdepending upon the temperature; and heat-emitting means arranged forheating at least a portion of said heat responsive elongated memberwhenever required.

6. In a vthermal circuit breaker, a thermally operable movable switchunit, comprising, in combination, a supporting member, a slightly curvedleaf spring member mounted at one end on said supporting member; acontact member mounted on the other end of said leaf spring member; aheat responsive electrically conductive elongated member secured at oneend to said other end of said leaf spring member 'and at its other endto said supporting member in the region of said one end of said slightlycurved leaf spring member, said heat responsive electrically conductiveelongated member adapted to be heated by passage of electric currenttherethrough and to change its length depending upon its temperature; anelectric circuit adapted to be connected to the end of said heatresponsive electrically conductive elongated member for heating the sameby passage of current therethrough; and separate heat-emitting meansarranged for heating at least a portion of said heat responsiveelectrically conductive elongated member whenever required.

7. In a thermal circuit breaker, a thermally operable movable switchunit, comprising, in combination, a supporting member, a slightly curvedleaf spring member mounted at one end on said supporting member; acontact member mounted on the other end of said leaf spring member; aheat responsive elongated member secured at one end to said other end ofsaid leaf spring member and at its other end to said supporting memberin the region of said one end of said slightly curved leaf springmember, said heat responsive elongated member changing its lengthdepending upon -the temperature; an electrically insulating layerarranged on at least a portion of said heat responsive elongated member;'and a thin electric current conducting layer arranged on saidelectrically insulating layer, said conducting layer Operating asheat-emitting means for said heat responsive elongated member.

8. T n a thermal circuit breaker, a thermally operable movable switchunit, comprising, in combination, a supporting member, a slightly curvedleaf spring member mounted at one end on said supporting member; acontact member mounted on the other end of said leaf spring member; vaheat responsive elongated member secured at one end to said other end ofl'said leaf spring member and at its other end to said supporting memberin the region of said one end of said slightly curved leaf springmember, said heat responsive elongated member changing its lengthdepending upon the temperature; an electrically insulating layerarranged on at least a portion of said heat responsive elongated member;a thin electric current conducting layer arra'nged on said electricallyinsulating layer; and means for sending a heating current through saidconducting layer.

OTTO WELTER.

